Information carrier and system for reading data stored on such an information carrier

ABSTRACT

The invention relates to a system for reading data stored on an information carrier ( 201 ), said system comprising: an optical element ( 202 ) for generating an array of light spots ( 203 ) from an input light beam ( 204 ), said array of light spots ( 203 ) being intended to scan said information carrier ( 201 ), a detector ( 205 ) for detecting said data from an array of output light beams generated by said information carrier ( 201 ) in response of said array of light spots ( 203 ). Use: Optical storage

FIELD OF THE INVENTION

The invention relates to a system for reading data stored on aninformation carrier.

The invention also relates to a reading apparatus comprising such asystem.

The invention also relates to an information carrier intended to be readby such system and reading apparatus.

The invention may be used in the field of optical data storage.

BACKGROUND OF THE INVENTION

Use optical storage is nowadays widespread for content distribution, forexample in storage systems based on the DVD (Digital Versatile Disk)standards. Optical storage has a big advantage over hard-disk andsolid-state storage in that information carriers are easy and cheap toduplicate.

However, due to the large amount of moving parts in the drives, knownapplications using this type of storage are not robust to shocks whenperforming read operations, considering the required stability of saidmoving parts during such operations. As a consequence, optical storagecannot easily be used in applications which are subject to shocks, suchas in portable devices.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to propose a new system for readingdata stored on an information carrier.

To this end, the system according to the invention for reading datastored on an information carrier comprises:

-   -   an optical element for generating an array of light spots from        an input light beam, said array of light spots being intended to        scan said information carrier,    -   a detector for detecting said data from an array of output light        beams generated by said information carrier in response of said        array of light spots.

This system includes a static information carrier (also called opticalcard) intended to store binary data organized in a data matrix. The bitson the information carrier are for example represented by transparentand non-transparent areas. Alternatively, the data are coded accordingto a multilevel approach.

The information carrier is intended to be illuminated not by a singlelight beam, but by an array of light spots generated by the opticalelement. The optical element corresponds advantageously to an array ofmicro-lenses, or to an array of apertures designed to exploit the Talboteffect.

Each light spot selects a specific area of data to be read on theinformation carrier, said data being detected by the detector. By movingthe optical element over the information carrier, the light spots canscan the entire information carrier.

Since the information carrier is static (i.e. motionless), the number ofmoving elements is highly reduced so that the system leads to a robustmechanical solution.

The system allows to use an information carrier which combines theadvantages of solid-state storage in that it is static, and theadvantages of optical storage in that it is removable from the readerapparatus which comprises the system.

In an embodiment, one pixel of the detector is intended to detect onedata of the information carrier. In a preferred embodiment, one pixel ofthe detector is intended to detect a set of data, each data from thisset of data being read successively by a single light spot. This allowsto circumvent the fact that pixels of the detector have a limited size,and to increase the storage capacity in a cost-effective manner.

In a preferred embodiment, the system according to the inventioncomprises an optical fiber plate (FP) stacked on said detector forcarrying said output light beams.

The advantage of using an optical fiber plate instead of an array oflenses is that cross-talk between two consecutive output light beams ishighly reduced, while the high numerical aperture of the fibers ensuresa large light collection efficiency. Data reading on the informationcarrier is thus improved.

It is also an object of the invention to propose a reading apparatus forreading data stored on an information carrier, said reading apparatuscomprising a system according to the invention.

It is also an object of the invention to propose an information carriercomprising an array of data arranged in macro-cells, each macro-celldata being intended to be read by a single light spot in the readingsystem according to the invention. The data are either represented bytransparent and non-transparent areas, by reflective and non-reflectiveareas, or advantageously represented in using a multilevel scheme inorder to increase the storage capacity of the information carrier.

According to a preferred embodiment, the information carrier is made ofadjacent elementary data areas having an hexagonal shape.

According to a preferred embodiment, the elementary data areas aregrouped so as to form an hexagonal lattice.

First, this allows to increase the data density of the informationcarrier. Secondly, since data density is increased, the scanningdistance between consecutive elementary data area is reduced, whichimplies an easier scanning mechanism. Finally, the distance between thelight spots may be increased, which results in a more robust bitdetection since crosstalk between adjacent elementary data area isreduced.

The invention also relates to various reading apparatus implementingsuch a reading system.

Detailed explanations and other aspects of the invention will be givenbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The particular aspects of the invention will now be explained withreference to the embodiments described hereinafter and considered inconnection with the accompanying drawings, in which identical parts orsub-steps are designated in the same manner:

FIG. 1 depicts a first system according to the invention,

FIG. 2 depicts a second system according to the invention,

FIG. 3 depicts a detailed view of components dedicated to macro-cellscanning used in systems according to the invention,

FIG. 4 illustrates the principle of macro-cell scanning according to theinvention,

FIG. 5 depicts an information carrier according to the invention,

FIG. 6A to FIG. 6C depict different types of elementary data areas in aninformation carrier according to the invention,

FIG. 7 depicts a three-dimensional view of the second system accordingto the invention,

FIG. 8 depicts a first arrangement for moving the systems according tothe invention over an information carrier,

FIG. 9 depicts a second arrangement for moving the systems according tothe invention over an information carrier,

FIG. 10 depicts detailed elements of the second arrangement for movingthe systems according to the invention over an information carrier,

FIG. 11 depicts a third system according to the invention,

FIG. 12 depicts a detailed view of the third system according to theinvention,

FIG. 13 depicts a three-dimensional view of the third system accordingto the invention,

FIGS. 14A and 14B illustrate elementary data areas having square andhexagonal shapes,

FIG. 15 depicts an improved information carrier according to theinvention where the macro-cells form a square lattice,

FIG. 16 depicts an improved information carrier according to theinvention where the macro-cells form an hexagonal lattice,

FIG. 17 illustrates various apparatus and devices comprising a systemfor reading an information carrier according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The system according to the invention aims at reading data stored on aninformation carrier. The information carrier is intended to store binarydata organized according to an array, as in a data matrix. If theinformation carrier is intended to be read in transmission, the statesof binary data stored on the information carrier are represented bytransparent areas and non-transparent areas (i.e. light-absorbing).Alternatively, if the information carrier is intended to be read inreflection, the states of binary data stored on the information carrierare represented by non-reflective areas (i.e. light-absorbing) andreflective areas. The areas are marked in a material such as glass,plastic or a material having magnetic properties.

The system according to the invention comprises:

-   -   an optical element for generating an array of light spots from        an input light beam, said array of light spots being intended to        scan said information carrier,    -   a detector for detecting said data from an array of output light        beams generated by said information carrier.

In a first embodiment depicted in FIG. 1, the system according to theinvention for reading data stored on an information carrier 101comprises an optical element 102 for generating an array of light spots103 from an input light beam 104, said array of light spots 103 beingintended to scan the information carrier 101.

The optical element 102 corresponds to a two-dimensional array ofmicro-lenses to the input of which the coherent input light beam 104 isapplied. The array of micro-lenses 102 is placed parallel and distantfrom the information carrier 101 so that light spots are focussed on theinformation carrier. The numerical aperture and quality of themicro-lenses determines the size of the light spots. For example, atwo-dimensional array of micro-lenses 102 having a numerical aperturewhich equals 0.3 can be used. The input light beam 104 can be realizedby a waveguide (not represented) for expanding an input laser beam, orby a two-dimensional array of coupled micro lasers.

The light spots are applied on transparent or non-transparent areas ofthe information carrier 101. If a light spot is applied on anon-transparent area, no output light beam is generated in response bythe information carrier. If a light spot is applied on a transparentarea, an output light beam is generated in response by the informationcarrier, said output light beam being detected by the detector 105. Thedetector 105 is thus used for detecting the binary value of the data ofthe area to which the optical spot is applied.

The detector 105 is advantageously made of an array of CMOS or CCDpixels. For example, one pixel of the detector is placed opposite anelementary data area containing one data (i.e. one bit) of theinformation carrier. In that case, one pixel of the detector is intendedto detect one data of the information carrier.

In a second embodiment depicted in FIG. 2, the system according to theinvention for reading data stored on an information carrier 201comprises an optical element 202 for generating an array of light spots203 from an input light beam 204, said array of light spots 203 beingintended to scan the information carrier 201.

The optical element 202 corresponds to a two-dimensional array ofapertures to the input of which the coherent input light beam 204 isapplied. The apertures correspond for example to circular holes having adiameter of 1 μm or much smaller. The input light beam 204 can berealized by a waveguide (not represented) for expanding an input laserbeam, or by a two-dimensional array of coupled micro lasers.

The light spots are applied to transparent or non-transparent areas ofthe information carrier 201. If a light spot is applied to anon-transparent area, no output light beam is generated in response bythe information carrier. If a light spot is applied to a transparentarea, an output light beam is generated in response by the informationcarrier, said output light beam being detected by the detector 205.Similarly as the first embodiment depicted in FIG. 1, the detector 205is thus used for detecting the binary value of the data of the area onwhich the optical spot is applied.

The detector 205 is advantageously made of an array of CMOS or CCDpixels. For example, one pixel of the detector is placed opposite anelementary data area containing a data of the information carrier. Inthat case, one pixel of the detector is intended to detect one data ofthe information carrier.

The array of light spots 203 is generated by the array of apertures 202in exploiting the Talbot effect which is a diffraction phenomenonworking as follows. When a coherent light beams, such as the input lightbeam 204, is applied to an object having a periodic diffractivestructure (thus forming light emitters), such as the array of apertures202, the diffracted lights recombine into identical images of theemitters at a plane located at a predictable distance z0 from thediffracting structure. This distance z0 is known as the Talbot distance.The Talbot distance z0 is given by the relation z0=2.n.d²/λ, where d isthe periodic spacing of the light emitters, λ is the wavelength of theinput light beam, and n is the refractive index of the propagationspace. More generally, re-imaging takes place at other distances z(m)spaced further from the emitters and which are a multiple of the Talbotdistance z such that z(m)=2.n.m.d²/λ, where m is an integer. Such are-imaging also takes place for m=½+an integer, but here the image isshifted over half a period. The re-imaging also takes place for m=¼+aninteger, and for m=¾+an integer, but the image has a doubled frequencywhich means that the period of the light spots is halved with respect tothat of the array of apertures.

Exploiting the Talbot effect allows to generate an array of light spotsof high quality at a relatively large distance from the array ofapertures 202 (a few hundreds of μm, expressed by z(m)), without theneed for optical lenses. This allows to insert for example a cover layerbetween the array of aperture 202 and the information carrier 201 toprevent the latter from contamination (e.g. dust, finger prints . . . ).Moreover, this facilitates the implementation and allows to increase ina cost-effective manner, compared to the use of an array ofmicro-lenses, the density of light spots which are applied to theinformation carrier.

FIG. 3 depicts a detailed view of the system according to the invention.It depicts a detector 305 which is intended to detect data from outputlight beams generated by the information carrier 301. The detectorcomprises pixels referred to as 302-303-304, the number of pixels shownbeing limited to facilitate the understanding. In particular, pixel 302is intended to detect data stored on the data area 306 of theinformation carrier, pixel 303 is intended to detect data stored on thedata area 307, and pixel 304 is intended to detect data stored on thedata area 308. Each data area (also called macro-cell) comprises a setof elementary data. For example, data area 306 comprises binary datareferred to as 306 a-306 b-306 c-306 d.

In this embodiment, one pixel of the detector is intended to detect aset of data, each elementary data among this set of data beingsuccessively read by a single light spot generated either by the arrayof micro-lenses 102 depicted in FIG. 1, or by the array of aperturesdepicted in FIG. 2. This way of reading data on the information carrieris called macro-cell scanning in the following.

FIG. 4, which is based on FIG. 3, illustrates by a non-limitativeexample the macro-cell scanning of an information carrier 401.

Data stored on the information carrier 401 have two states indicatedeither by a black area (i.e. non-transparent) or white area (i.e.transparent). For example, a black area corresponds to a “0” binarystate while a white area corresponds to a “1” binary state.

When a pixel of the detector 405 is illuminated by an output light beamgenerated by the information carrier 401, the pixel is represented by awhite area. In that case, the pixel delivers an electric output signal(not represented) having a first state. On the contrary, when a pixel ofthe detector 405 does not receive any output light beam from theinformation carrier, the pixel is represented by a cross-hatched area.In that case, the pixel delivers an electric output signal (notrepresented) having a second state.

In this example, each set of data comprises four elementary data, and asingle light spot is applied simultaneously to each set of data. Thescanning of the information carrier 401 by the light spots 403 isperformed for example from left to right, with an incremental lateraldisplacement which equals the distance between two elementary data.

In position A, all the light spots are applied to non-transparent areasso that all pixels of the detector are in the second state.

In position B, after displacement of the light spots to the right, thelight spot to the left is applied to a transparent area so that thecorresponding pixel is in the first state, while the two other lightspots are applied to non-transparent areas so that the two correspondingpixels of the detector are in the second state.

In position C, after displacement of the light spots to the right, thelight spot to the left is applied to a non-transparent area so that thecorresponding pixel is in the second state, while the two other lightspots are applied to transparent areas so that the two correspondingpixels of the detector are in the first state.

In position D, after displacement of the light spots to the right, thecentral light spot is applied to a non-transparent area so that thecorresponding pixel is in the second state, while the two other lightspots are applied to transparent areas so that the two correspondingpixels of the detector are in the first state.

The scanning of the information carrier 401 is complete when the lightspots have been applied to all data of a set of data facing a pixel ofthe detector. It implies a two-dimensional scanning of the informationcarrier. Elementary data which compose a set of data opposite a pixel ofthe detector are read successively by a single light spot.

FIG. 5 represents a top view of an information carrier according to theinvention. This information carrier comprises a plurality of adjacentmacro-cells (M1, M2, M3, . . . ), each macro-cell comprising a set ofelementary data areas (EDA1, EDA2, . . . ). In this example, eachmacro-cell comprises 16 elementary data areas. To facilitates thescanning of a macro-cell, the elementary data areas are advantageouslyare placed adjacent and arranged according to a matrix, and have asquare shape.

Each macro-cell is intended to be read by a single light spot, inscanning successively said single light spot over all elementary dataareas of said macro-cell. The width of the light spot intended to beapplied on each macro-cell is advantageously equal to the width of theelementary data areas, so that a maximum of light intensity is detectedby the pixels of the detector.

According to a simple solution, each elementary data area is intended tostore one binary data. To this end, each elementary data may berepresented by a transparent (i.e. light non-absorbing) andnon-transparent areas (i.e. light absorbing), or alternatively byreflective and non-reflective areas.

Alternatively, the data may be coded according to a multilevel scheme inorder to increase the data density of the information carrier. To thisend, instead of defining each elementary data area by only two levels oflight propagation, it is proposed to define each elementary data area byN levels, where N might advantageously be a power of 2. In this case, itis assumed that ²log(N) bits (²log being the binary logarithm operator)can be coded per elementary data area. For example, if N=4, it becomespossible to store a 2-bits data in each elementary data area, thusdoubling the storage capacity on the information carrier.

FIG. 6A illustrates a first solution of a two-levels data coding in anelementary data area EDA (N=4 in this case). The elementary data areacomprises a layer made of a material characterized by alight-transmission percentage LT. The percentage LT is taken among a setof 4 values, depending on the value of the 2-bits data to be coded Forexample:

-   -   a first value of LT=5% may be used to encode a 2-bits data which        value is 00,    -   a second value of LT=35% may be used to encode a 2-bits data        which value is 01,    -   a third value of LT=65% may be used to encode a 2-bits data        which value is 10,    -   a fourth value of LT=95% may be used to encode a 2-bits data        which value is 11,        As a consequence, a light spot which passes through an        elementary data area is converted by a detector pixel into an        electrical signal which may take 4 different levels. By the use        of three thresholds (or N−1 thresholds generally speaking)        applied to this electrical signal, the 2-bits data can easily be        recovered.

It is noted that the percentage LT can be defined in changing thelight-transmission coefficient of the material (4 different coefficientsare thus potentially defined), or alternatively in changing thethickness of the elementary data area while using a material having agiven light-transmission coefficient (4 different thicknesses are thuspotentially defined).

The layer may be made of a dye material as that used in CD-R and DVD-Rdisks. Alternatively, the layer may be made of a metal layers (e.g.chromium or aluminium) whose thickness is varied for defining a variablelight-transmitting layer.

FIG. 6B depicts a second solution of a two-levels data coding in anelementary data area EDA (N=4 in this case). The elementary data areacomprises a layer made of a non-transparent material (i.e. lightabsorbing). Two cases have to be considered.

First, if the information carrier is used in a transmission mode, theelementary data area also comprises an aperture letting the light spotpass through it

Secondly, if the information carrier is used in a reflection mode, theelementary data area also comprises a reflecting surface so that thelight spot is partially reflected.

The aperture (or alternatively the reflecting surface) may be expressedas a percentage AS of the total surface of the elementary data area EDA.The percentage AS is taken among a set of 4 values, depending on thevalue of the 2-bits data to be coded. For example:

-   -   a first value of AS=5% may be used to encode a 2-bits data which        value is 00,    -   a second value of AS=35% may be used to encode a 2-bits data        which value is 01,    -   a third value of AS=65% may be used to encode a 2-bits data        which value is 10,    -   a fourth value of AS=95% may be used to encode a 2-bits data        which value is 11,        As a consequence, a light spot which passes through an        elementary data area is converted by a detector pixel into an        electrical signal which may take 4 different levels. By the use        of three thresholds (or N−1 thresholds generally speaking)        applied to this electrical signal, the 2-bits data can easily be        recovered.

The layer may be made of any material (e.g. aluminium, plastic . . . )on which apertures or reflecting areas of variable surfaces areincluded.

FIG. 6C illustrates a third solution of a two-levels data coding in anelementary data area EDA (N=4 in this case). The elementary data areacomprises a layer made of a polarized material whose polarizationorientation (illustrated by the two-directional arrow) is characterizedby an angle φ. The angle φ is taken among a set of 4 values, dependingon the value of the 2-bits data to be coded. For example:

-   -   a first value of φ=0° may be used to encode a 2-bits data which        value is 00,    -   a second value of φ=30° may be used to encode a 2-bits data        which value is 01,    -   a third value of φ=60° may be used to encode a 2-bits data which        value is 10,    -   a fourth value of φ+=90° may be used to encode a 2-bits data        which value is 11,        As a consequence, a light spot which passes through an        elementary data area is converted by a detector pixel into an        electrical signal which may take 4 different levels. By the use        of three thresholds (or N−1 thresholds generally speaking)        applied to this electrical signal, the 2-bits data can easily be        recovered.

The light spots applied to the information carrier must be polarizedaccording to a given and fixed direction.

The layer may be made of a polarized material corresponding to a liquidcrystal (LC) element. The polarization direction may for example bevaried by varying the thickness of this material.

FIG. 7 depicts a three-dimensional view of the system as depicted inFIG. 2. It comprises an array of apertures 702 for generating an arrayof light spots applied to the information carrier 701. Each light spotis applied and scanned over a two-dimensional set of data of theinformation carrier 701 (represented by bold squares). In response tothis light spot, the information carrier generates (or not, if the lightspot is applied to a non-transparent area) an output light beam inresponse, which is detected by the pixel of the detector 703 oppositethe set of data which is scanned. The scanning of the informationcarrier 701 is performed in displacing the array of apertures 702 alongthe x and y axes.

The array of apertures 702, the information carrier 701 and the detector703 are stacked in parallel planes. The only moving part is the array ofapertures 702.

It is noted that the three-dimensional view of the system as depicted inFIG. 1 would be the same as the one depicted in FIG. 7 in replacing thearray of apertures 702 by the array of micro-lenses 102.

The scanning of the information carrier by the array of light spots isdone in a plane parallel to the information carrier. A scanning deviceprovides translational movement of the light spots in the two directionsx and y for scanning all the surface of the information carrier.

In a first solution depicted in FIG. 8, the scanning device correspondsto an H-bridge. The optical element generating the array of light spots(i.e. the array of micro-lenses or the array of apertures) isimplemented in a first sledge 801 which is movable along the y axiscompared to a second sledge 802. To this end, the first sledge 801comprises joints 803-804-805-806 in contact with guides 807-808. Thesecond sledge 802 is movable along the x axis by means of joints811-812-813-814 in contact with guides 809-810. The sledges 801 and 802are translated by means of actuators (not represented), such as bystep-by-step motors, magnetic or piezoelectric actuators acting asjacks.

In a second solution depicted in FIG. 9, the scanning device ismaintained in a frame 901. The elements used for suspending the frame901 are depicted in a detailed three-dimensional view in FIG. 10. Theseelements comprise:

-   -   a first leaf spring 902,    -   a second leaf spring 903,    -   a first piezoelectric element 904 providing the actuation of the        scanning device 901 along the x axis,    -   a second piezoelectric element 905 providing the actuation of        the scanning device 901 along the y axis.

The second solution depicted in FIG. 9 has less mechanical transmissionsthan the H-bridge solution depicted in FIG. 8. The piezoelectricelements, in contact with the frame 901, are electrically controlled(not represented) so that a voltage variation results in a dimensionchange of the piezoelectric elements, leading to a displacement of theframe 901 along the x and/or the y axis.

The position Pos1 depicts the scanning device 901 in a first position,while the position Pos2 depicts the scanning device 901 in a secondposition after translation along the x axis. The flexibility of the leafsprings 902 and 903 is put in evidence.

A similar configuration can be built with four piezoelectric elements,the two extra piezoelectric elements replacing the leaf springs 902 and903. In that case, opposite pair of piezoelectric elements act togetherin one direction in the same way as an antagonistic pair of muscles.

In a third embodiment depicted in FIG. 11, the system according to theinvention comprises an optical fiber plate FP stacked on the detector DTfor carrying the output light beams OLB generated at the output of theinformation carrier IC The output light beams OLB are derived from thearray of light spots generated by the array of apertures AA and appliedto the information carrier IC. The optical fiber plate FP is thusintended to be inserted between the information carrier and thedetector.

The optical fiber plate FP consists of a multitude of cylindricaloptical fiber elements bundled in parallel together in a glass plate(for example, but not necessarily, by using glue), and polished into anoptical plate having two flat sides. A light distribution at one end ofthe plate is thus carried through the fibers to the other side of theplate without cross-talk. Typically, the pitch of the fibers is on theorder of a few microns, the numerical aperture of the fibers is 1 andtheir transmission efficiency is for example in the range 70-80%.

The optical fiber plate FP is placed as close as possible to thedetector DT for limiting cross-talk at the output of the fibers.

Advantageously, a protection layer PL (represented cross-hatched) isinserted between the optical fiber plate FP and the detector DT, formechanically strengthening the detector and protecting the sensitivearea of each pixel constituting the detector. Moreover, this allows theoptical fiber plate FP, the protection layer PL and the detector DT tobe fixed together for example by means of glue or pressed by a clampsystem (not shown), defining as a consequence a single unit intended tobe placed above the information carrier IC.

The optical fiber plate FP is characterized by its fiber density definedas the number of fibers per unit area. Basically, one fiber faces onepixel of the detector. Advantageously, a plurality of fibers face onepixel of the detector (as represented in FIG. 1), which avoid to definean accurate alignment between the fibers and the pixels of the detector.

FIG. 12 depicts a detailed view of the third system according to theinvention. In particular, it is depicted that the detector DT comprises:

-   -   a plurality of pixels S1-S9 (this number being given as an        example), each pixel comprising a sensitive area SA1-SA9,        respectively, for converting incident light into an electrical        signal.    -   a first metallization layer ML1, a second metallization layer        ML2 and a third metallization layer ML3 which are part of the        standard CMOS design, and play here an additional role in        reducing cross-talk.

The protection layer PL is stacked on the detector DT so thatmetallization layers are protected, which ensures a stable quality ofdetection in the long term. Since the protection layer and the detectorcan form a single unit, it can be considered that the optical fiberplate FP and the detector DT are stacked.

Advantageously, an array of micro-lenses ML is inserted between theoptical fiber plate FP and the detector for converging the light beamsgenerated at the output of the fibers towards the sensitive areasSA1-SA9 of each pixel. Each micro-lens faces one pixel of the detector.The cross-talk at the output of the optical fiber plate is thus reduced.

FIG. 13 depicts a three-dimensional view of the third system accordingto the invention.

Alternatively, in a preferred embodiment according to the invention, theelementary data areas of the information carrier no longer define squareshapes, but hexagonal shapes. Compare to the use of square shapes,hexagonal shapes leads to significant advantages as discussed in thefollowing.

FIG. 14A depicts two adjacent elementary data areas having square shapesas described previously, while FIG. 14B depicts two adjacent elementarydata areas having hexagonal shapes.

Concerning FIG. 14A, the surface as of each elementary data area, thedistance d_(S) between the centres of two adjacent elementary dataareas, and the maximum distance r_(S) separating the centre of anelementary data area and an adjacent elementary data, are expressed bythe following relations:a _(S)=2r _(S) ²  (1)a _(S) =d _(S) ²  (2)d _(S)=√{square root over (2)}.r_(S)  (3)

Concerning FIG. 14B, the surface a_(H) of each elementary data area, thedistance d_(H) between the centres of two adjacent elementary dataareas, and the maximum distance r_(H) separating the centre of anelementary data area and an adjacent elementary data, are expressed bythe following relations: $\begin{matrix}{a_{H} = {\frac{3}{2}{\sqrt{3} \cdot r_{H}^{2}}}} & (4) \\{a_{H} = {\frac{\sqrt{3}}{2} \cdot d_{h}^{2}}} & (5) \\{d_{H} = {\sqrt{3} \cdot r_{H}}} & (6)\end{matrix}$

Storage capacity of the information carrier is eventually limited by thespot size. The minimum achievable spot size dictates the minimumrequired separation between the elementary data areas. If the separationis too small, there will be overlap of the spot on neighbouring bits(so-called cross talk or inter-symbol interference) and bit detectionwill be difficult. The storage capacity of the information carrier(either having square or hexagonal elementary data areas) is thusdetermined in calculating how many bits per square inch can be storedfor a given bit separation. Having a given bit separation is expressedby the relation d_(H)=d_(S). Which such a relation, the ratioa_(S)/a_(H) may be expressed from (5) and (2) by the following relation:$\begin{matrix}{\frac{a_{S}}{a_{H}} = {\frac{2}{\sqrt{3}} \approx 1.15}} & (7)\end{matrix}$This indicates that the data density of the information carrier (in bitsper elementary data area) may be increased by 15% if an hexagonallattice is used instead of a square lattice.

Advantageously, the elementary data areas may be arranged according toadjacent macro-cells also having hexagonal shape. If the area A_(H) ofthe hexagonal macro-cells is chosen so as to equal the area A_(S) of thesquare macro-cells, then the ratio D_(H)/D_(S) may be expressed by thefollowing relation: $\begin{matrix}{\frac{D_{H}}{D_{S}} = {\sqrt{\frac{2}{\sqrt{3}}} \approx 1.07}} & (8)\end{matrix}$

where D_(H) is the distance between the centres of two adjacenthexagonal macro-cells,

-   -   D_(S) is the distance between the centres of two adjacent square        macro-cells.        This means that for the same light spots density, the light        spots separation, i.e. the distance between the centre of two        adjacent macro-cells, is 7% larger when the macro-cells are        hexagonal, making the bit detection more robust since crosstalk        between adjacent elementary data area is reduced.

FIG. 15 represents a top view of an improved information carrieraccording to the invention comprising a plurality of adjacentmacro-cells (M1, M2, M3, . . . ) each having a square shape, eachmacro-cell comprising a set of elementary data areas (EDA1, EDA2, . . .) each having an hexagonal shape. In this example, each macro-cellcomprises 16 elementary data areas. To facilitates the scanning of amacro-cell, the elementary data areas are advantageously placedadjacent.

FIG. 16 represents a top view of an improved information carrieraccording to the invention comprising a plurality of adjacentmacro-cells (M1, M2, M3, . . . ) each having an hexagonal shape, eachmacro-cell comprising a set of elementary data areas (EDA1, EDA2, . . .) each having an hexagonal shape. In this example, each macro-cellcomprises 55 elementary data areas. To facilitates the scanning of amacro-cell, the elementary data areas are advantageously placedadjacent.

As illustrated in FIG. 17, the system according to the invention mayadvantageously be implemented in a reading apparatus RA (e.g. homeplayer apparatus . . . ), a portable device PD (e.g. portable digitalassistant, portable computer, a game player unit . . . ), or a mobiletelephone MT. These apparatus and devices comprise an opening (OP)intended to receive an information carrier 1701 according to theinvention, and a reading system in view of recovering data stored onsaid information carrier.

Use of the verb “comprise” and its conjugations does not exclude thepresence of elements or steps other than those stated in the claims. Useof the article “a” or “an” preceding an element or step does not excludethe presence of a plurality of such elements or steps.

1. System for reading data stored on an information carrier (101-201), said system comprising: an optical element (102-202) for generating an array of light spots (103-203) from an input light beam (104-204), said array of light spots (103-203) being intended to scan said information carrier (101-201), a detector (105-205) for detecting said data from an array of output light beams generated by said information carrier (101-201) in response of said array of light spots (103-203).
 2. System as claimed in claim 1, wherein the optical element (102-202) is an array of lenses (102) or an array of apertures (202).
 3. System as claimed in claim 1, wherein the detector (105-205) comprises an array of pixels, each pixel being intended to detect a plurality of data stored on the information carrier (101-201).
 4. System as claimed in claim 1, comprising an optical fiber plate (FP) stacked on said detector for carrying said output light beams.
 5. System as claimed in claim 4, comprising an array of micro-lenses (ML) inserted between said optical fiber plate (FP) and said detector, each micro-lens facing a pixel of the detector.
 6. System as claimed in claim 1, comprising means for shifting the optical element (102-202) over the information carrier (101-201).
 7. Reading apparatus for reading data stored on an information carrier, said reading apparatus comprising a system as claimed in claim
 1. 8. Information carrier comprising a plurality of adjacent macro-cells (M1, M2, M3 . . . ), each macro-cell comprising a set of elementary data areas (EDA1, EDA2 . . . ).
 9. Information carrier as claimed in claim 8, wherein each of said elementary data areas (EDA1, EDA2 . . . ) is made of a layer intended to define at least two light-reflecting levels.
 10. Information carrier as claimed in claim 8, wherein each of said elementary data areas (EDA1, EDA2 . . . ) is made of a layer intended to define at least two light-absorbing levels.
 11. Information carrier as claimed in claim 10, wherein said layer is made of a material having a variable light-transmission coefficient for defining said levels.
 12. Information carrier as claimed in claim 10, wherein said layer has a variable thickness for defining said levels.
 13. Information carrier as claimed in claim 10, wherein said layer comprises an aperture of variable surface for defining said levels.
 14. Information carrier as claimed in claim 10, wherein said layer is made of a light-polarized material whose polarization orientation is variable for defining said levels.
 15. Information carrier as claimed in claim 9, wherein said layer comprises a reflecting area of variable surface for defining said levels.
 16. Information carrier as claimed in claim 8, wherein said macro-cells (M1, M2, M3 . . . ) have a square shape.
 17. Information carrier as claimed in claim 8, wherein said macro-cells (M1, M2, M3 . . . ) have an hexagonal shape.
 18. Information carrier as claimed in claim 17, wherein said elementary data areas (EDA1, EDA2 . . . ) have a square shape or an hexagonal shape.
 19. A portable device comprising a system as claimed in claim
 1. 20. A mobile telephone comprising a system as claimed in claim
 1. 21. A game player unit comprising a system as claimed in claim
 1. 